1. Field of the Invention
The present invention relates to a process for the conversion of hydrocarbon feed stocks. More particularly, this invention relates to a catalytic process for the hydroisomerization of saturated acyclic and alicyclic hydrocarbons in a reaction zone comprising at least one temperature zone, the temperature in at least one zone being controlled by autorefrigeration.
2. Description of the Prior Art
Hydrocarbon conversion processes involving the use of metal halide based catalysts have been extensively described in the prior art. For example, U.S. Pat. Nos. 2,683,763 and 2,683,764 disclose that tantalum pentalfuoride or columbium (niobium) pentafluoride in combination with hydrogen fluoride can be used to refine hydrocarbon oils or to promote the disproportionation of alkyl-substituted aromatic materials. The patents also teach that hydrogen fluoride/tantalum pentafluoride and hydrogen fluoride/columbium pentafluoride are powerful catalysts for isomerization, alkylation, cracking and other reactions of aromatics. U.S. Pat. No. 3,201,494, teaches that niobium pentafluoride or tantalum pentafluoride in combination with hydrofluoric acid can be employed for the isomerization or purified hexane feed stocks. More recently, application No. 445,163, filed Feb. 25, 1974, which issued as U.S. Pat. No. 3,948,761 discloses a process for hydroiosomerizing saturated alicyclic and acyclic hydrocarbons in the presence of a catalysts comprising a difficultly reducible metal halide in combination with at least a molar equivalent of hydrogen halide. The isomerization of hydrocarbons using more than one temperature zone to form an isomerate of enhanced octane is also known in the art (see for example U.S. Pat Nos. 3,054,832 and 3,201,494). In addition, it is known that it is necessary to remove the heat evolved during isomerization to maintain the reaction temperature at a desired level. This may be accomplished by interstage cooling using water or a refrigerant, pump-around cooling and the like (see for example U.S. Pat. No. 3,541,181).
However, none of the foregoing prior art teaches a hydroisomerization process having one or more temperature zones wherein the temperature in at least one zone is controlled by autorefrigeration, thereby eliminating the need for indirect heat exchange to remove the exothermic heat of reaction and to form an isomerate of enhanced octane.